DIFFERENTIAL EXPRESSION OF GENES OF PSEUDOMONAS-SYRINGAE ON LEAVES AND IN CULTURE EVALUATED WITH RANDOM GENOMIC LUX FUSIONS

Differential expression of genes of Pseudomonas syringae strain B728a on plants and in culture was assessed by measuring light production by a large collection of mutant strains containing random genomic insert ions of a promoterless lux operon. Reporter gene fusions were made usi ng Tn4431 containing luxCDABE from Vibrio fisheri. Light production re producibly increased seven-fold when n-decanal was added to cells harv ested from plant surfaces, to over 800-fold when added to cells cultur ed on a solidified culture medium, thus increasing the sensitivity of this reporter gene system. One of the 173 mutants tested exhibited sig nificantly higher light production on plants than on solidified cultur e media compared to other mutants, while one lux fusion-containing str ain produced significantly more light on culture media than on plants relative to the other mutants. The plant-inducible genes identified we re not required for pathogenicity of this strain. Approximately 2% of the genes of P. syringae are apparently transcribed more actively in c ells growing epiphytically on plants than in common culture media indi cating that bacterial cells on plants may have substantially different behaviours than that of cultured cells.